1. Field of the Invention
This invention relates to a semiconductor light emitting device and its manufacturing method, especially suitable for application to a semiconductor light emitting device using II-VI compound semiconductors.
2. Description of the Related Art
ZnSe-based II-VI compound semiconductors are used in semiconductor light emitting devices, such as semiconductor lasers and light emitting diodes for emitting blue to green light. In semiconductor light emitting devices using II-VI compound semiconductors, p-type layers with sufficiently high carrier concentrations have not been obtained, and they involved the problems of a high contact resistance of the p-side electrode and a high operation voltage.
More specifically, in a semiconductor light emitting device using an Au electrode, as the p-side electrode, in contact with a p-type ZnSe layer, for example, its operation voltage is as high as decades volt. To decrease the operation voltage, a technology has been proposed, which stacks a p-type ZnSe/ZnTe multiquantum well (MQW) layer on a p-type ZnSe layer, subsequently stacks a p-type ZnTe layer promising a carrier concentration as high as 1.times.10.sup.19 cm.sup.-3, and then makes a p-side electrode, in particular, a p-side electrode made by sequentially stacking a Pd film, Pt film and Au film, in contact with the p-type ZnTe layer. Certainly, the technology greatly improved the ohmic contact characteristics of the p-side electrode, and has decreased the operation voltage to 3 to 4 V. However, the p-side electrode contact structure using the p-type ZnSe/ZnTe MQW layer is unstable, and its reproducibility is still unacceptable. Moreover, it has been observed that the operation voltage increases during operation of the semiconductor light emitting device.
On the other hand, for the purpose of reducing the threshold current, a semiconductor light emitting device includes a current blocking means to locally block a current and locally concentrate the current to the oscillation region of the active layer so as to form a structure having a gain-guide function, in which the carrier concentration is locally high, that is, the gain suddenly increases in a limited location. For making such a gain guide semiconductor light emitting device, a typical way of current blocking is to selectively make a high-resistance region by ion implantation of proton, boron, or the like, such that a limited current path be formed.
However, II-VI compound semiconductors, in general, are more liable to damages by ion implantation than III-V compound semiconductors. Therefore, if a semiconductor light emitting device using II-VI compound semiconductors is processed for current blocking by ion implantation, damages by ion implantation cause degradation of its characteristics, such as degradation in reliability, and make it difficult to obtain the current blocking region with an acceptable reproducibility and reliability.